Abstract Kidneys, as a major organ for waste removal, are being exploited to accelerate the body clearance of ?off-target? engineered nanoparticles to meet FDA regulation for the clinical translation of nanomedicines, which demands thorough understanding of nanoparticle transport and interactions at the fundamental level. However, renal proximal tubule is often overlooked in comparison with extensive studies on glomerular filtration of engineered nanoparticles even though proximal tubule is the most active site involved in concentration, retention and reabsorption of the filtered proteins through glomeruli. While the sizes and charges are recognized important in protein reabsorption due to unique microvilli-covered surface of proximal tubule cells, it is still largely unknown how engineered nanoparticles will be retained and interact with the proximal tubules after being filtered through the glomeruli. The objective of this application is to advance our fundamental understanding of the size, charge and surface chemistry effects on the transport and interactions of engineered nanoparticles in not only the normal but also injured proximal tubules; so that we can obtain a general strategy in minimizing their potential health hazards in their future clinical applications. Five specific aims are proposed to accomplish the objective: In Aims 1-3, we will unravel size, surface chemistry, and surface charge effects on the transport and interaction of renal clearable gold nanoparticle in renal proximal tubules. Aim 4 is to revisit these size, charge and surface chemistry dependencies in the diseased kidneys with proximal tubular injury. Aim 5 is to evaluate biocompatibility and nephrotoxicity of renal clearable AuNPs with distinct interactions with proximal tubules in both normal mice and mice with proximal tubular injury. Success of the proposed studies will significantly advance our fundamental understanding of in vivo interactions of engineered nanoparticles with renal proximal tubules, laying down a solid foundation for further development of new design strategies that can minimize nephrotoxicity of nanomedicines in their future clinical translation.